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  <div class="section" id="s-postgresql-specific-lookups">
<span id="postgresql-specific-lookups"></span><h1>PostgreSQL 特有查找<a class="headerlink" href="#postgresql-specific-lookups" title="永久链接至标题">¶</a></h1>
<div class="section" id="s-trigram-similarity">
<span id="trigram-similarity"></span><h2>三元相似度<a class="headerlink" href="#trigram-similarity" title="永久链接至标题">¶</a></h2>
<p id="std:fieldlookup-trigram_similar"><code class="docutils literal notranslate"><span class="pre">trigram_similar</span></code> 允许你使用专用的 PostgreSQL 扩展来执行三元查找，测量共享的 trigram（三个连续字符）的数量。给定一个表达式进行三元查找，并返回相似度测量大于当前相似度阈值的结果。</p>
<p>要使用它，请在你的 <a class="reference internal" href="../../settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal notranslate"><span class="pre">INSTALLED_APPS</span></code></a> 中添加 <code class="docutils literal notranslate"><span class="pre">'django.contrib.postgres'</span></code>，并激活 PostgreSQL 上的 <a class="reference external" href="https://www.postgresql.org/docs/current/pgtrgm.html">pg_trgm 扩展</a> 。你可以使用 <a class="reference internal" href="operations.html#django.contrib.postgres.operations.TrigramExtension" title="django.contrib.postgres.operations.TrigramExtension"><code class="xref py py-class docutils literal notranslate"><span class="pre">TrigramExtension</span></code></a> 迁移操作来安装该扩展。</p>
<p><code class="docutils literal notranslate"><span class="pre">trigram_similar</span></code> 查找可以用于 <a class="reference internal" href="../../models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><code class="xref py py-class docutils literal notranslate"><span class="pre">CharField</span></code></a> 和 <a class="reference internal" href="../../models/fields.html#django.db.models.TextField" title="django.db.models.TextField"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextField</span></code></a>：</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">City</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">name__trigram_similar</span><span class="o">=</span><span class="s2">&quot;Middlesborough&quot;</span><span class="p">)</span>
<span class="go">[&#39;&lt;City: Middlesbrough&gt;&#39;]</span>
</pre></div>
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<div class="section" id="s-unaccent">
<span id="unaccent"></span><h2><code class="docutils literal notranslate"><span class="pre">Unaccent</span></code><a class="headerlink" href="#unaccent" title="永久链接至标题">¶</a></h2>
<p id="std:fieldlookup-unaccent"><code class="docutils literal notranslate"><span class="pre">unaccent</span></code> 查找允许你使用一个专门的 PostgreSQL 扩展来执行不区分重音的查找。</p>
<p>这个查询是用 <a class="reference internal" href="../../models/lookups.html#django.db.models.Transform" title="django.db.models.Transform"><code class="xref py py-class docutils literal notranslate"><span class="pre">Transform</span></code></a> 来实现的，所以它可以和其他查询函数连锁使用。要使用它，你需要在你的 <a class="reference internal" href="../../settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal notranslate"><span class="pre">INSTALLED_APPS</span></code></a> 中添加 <code class="docutils literal notranslate"><span class="pre">'django.contrib.postgres'</span></code>，并激活 PostgreSQL 上的 <a class="reference external" href="https://www.postgresql.org/docs/current/unaccent.html">unaccent 扩展</a> 。如果你想使用迁移来进行这个激活，可以使用 <a class="reference internal" href="operations.html#django.contrib.postgres.operations.UnaccentExtension" title="django.contrib.postgres.operations.UnaccentExtension"><code class="xref py py-class docutils literal notranslate"><span class="pre">UnaccentExtension</span></code></a> 迁移操作。</p>
<p><code class="docutils literal notranslate"><span class="pre">unaccent</span></code> 查找可以用在 <a class="reference internal" href="../../models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><code class="xref py py-class docutils literal notranslate"><span class="pre">CharField</span></code></a> 和 <a class="reference internal" href="../../models/fields.html#django.db.models.TextField" title="django.db.models.TextField"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextField</span></code></a> 上：</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">City</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">name__unaccent</span><span class="o">=</span><span class="s2">&quot;México&quot;</span><span class="p">)</span>
<span class="go">[&#39;&lt;City: Mexico&gt;&#39;]</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">User</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">first_name__unaccent__startswith</span><span class="o">=</span><span class="s2">&quot;Jerem&quot;</span><span class="p">)</span>
<span class="go">[&#39;&lt;User: Jeremy&gt;&#39;, &#39;&lt;User: Jérémy&gt;&#39;, &#39;&lt;User: Jérémie&gt;&#39;, &#39;&lt;User: Jeremie&gt;&#39;]</span>
</pre></div>
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<div class="admonition warning">
<p class="first admonition-title">警告</p>
<p class="last"><code class="docutils literal notranslate"><span class="pre">unaccent</span></code> 查找在大多数使用情况下应该可以正常进行。但是，使用该过滤器的查询一般会进行全表扫描，这对大表来说可能很慢。在这些情况下，使用专门的全文索引工具可能是合适的。</p>
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<li><a class="reference internal" href="#">PostgreSQL 特有查找</a><ul>
<li><a class="reference internal" href="#trigram-similarity">三元相似度</a></li>
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